1. Field of the Invention
The present invention relates generally to a control system for automotive automatic air conditioners. More specifically, the invention relates to a system for automatically controlling discharge air temperature and discharge air flow rate in automotive air conditioners.
2. Description of the Prior Art
Automotive air conditioners generally produce air flow due to rotation of a blower which is disposed within a duct body at a location near inlets thereof. The air flow produced by the blower passes through an evaporator of a cooler unit. Thereafter, a part of the air flow passes through a heater core or heat exchanger of a heater unit to be supplied to an air mix chamber and the rest thereof is directly supplied to the air mix chamber. The conditioning air is selectively discharged from a chest vent, foot vent or defroster nozzle. An air-mix door is pivotably provided between the evaporator and the heater core so that the ratio of the air flow passing through the heater core to the air flow by passing the heater core is determined by the opening angle of the air-mix door. Therefore, in such automotive air conditioners, discharge air temperature and air flow rate are determined by the opening angle of the air-mix door and by the operation voltage applied to the blower, respectively.
The opening angle of the air-mix door and the blower voltage are determined by control parameters, such as a manually selectable target temperature, atmospheric temperature, the air temperature in the vehicular cabin, insolation and so forth. When the cabin temperature is relatively high, the air discharge rate is made relatively large in order to rapidly decrease the cabin temperature. As the cabin temperature decreases, the temperature of the discharge air decreases. Therefore, the blower voltage is decreased gradually as the temperature of the vehicular cabin decreases in order to prevent the cabin temperature from becoming lower than the target temperature. Accordingly, the operation voltage applied to the blower is designed to be a minimal value V.sub.LO when the difference between the cabin temperature and the target temperature is lower than a predetermined value.
In such types of control systems for air conditioners, the occupant in the vehicular cabin may feel that the discharge air flow is too cool when he is directly exposed to the discharge air flow, since the discharge air temperature is very much cooler than the cabin temperature.